FIG. 11 is a construction diagram showing a pilot nozzle of a conventional gas turbine combustor. A combustor in a gas turbine is a portion that mixes fuel with high-temperature compressed air from a compressor, to combust the fuel. This combustor has a main nozzle (not shown) for carrying out main combustion, and a pilot nozzle 30 for maintaining a flame that becomes a pilot near the main nozzle, disposed inside its internal cylinder.
The pilot nozzle 30 is supplied with a pilot fuel like fuel oil or fuel gas from a rear end portion 31. Among the pilot fuels supplied, the fuel oil passes through a fuel oil supply pipe 33 that is disposed to pierce through the center of a heat-shielding air layer 32 in its axial direction that is provided along the axial core portion, and the fuel is jetted from a front end nozzle 34. Further, the inside of the pilot nozzle also has a structure for supplying an atomized fluid to diffuse the jetting of the fuel, and jetting the fluid from the front end.
FIG. 12 is a cross-sectional view showing the front end portion of the nozzle shown in FIG. 11. The pilot nozzle 30 has a concentric circular multi-layer structure. In other words, the fuel oil supply pipe 33, heat-shielding air layer 32, internal cylinder 35, atomized-fluid supply path 36, and the external cylinder 37 are concentrically combined together from the inside. Further, a pilot nozzle of what is called a duel-fuel system that uses fuel oil and fuel gas by switching between them or uses both as pilot fuel, has had a three-layer structure. Namely, a gas supply pipe 38 is concentrically combined with the fuel oil supply pipe 33 at the further outer side of the external cylinder 37, and this supply pipe 38 is sealed with an exterior cylinder 39.
As explained above, the pilot nozzle 30 is exposed to the high-temperature compressed air, and receives thermal conduction from the external surface. On the other hand, the fuel oil that flows through the inside of the fuel oil supply pipe at the pilot nozzle axial core portion has a lower temperature than the temperature of this air. Therefore, there arises a difference between the thermal expansion of the external cylinder of the pilot nozzle and the thermal expansion of the fuel oil supply pipe in proportion to this temperature difference. Consequently, there has been a problem that when this difference in the thermal expansion is large, a position of the jet nozzle at the front end changes, and this gives bad influence to a state of the diffusion of the jetted fuel.
Further, when the fuel gas is not used, the thermal conduction from the high-temperature compressed air at the outside of the pilot nozzle gives particularly large influence to the fuel oil at the axial core portion. This brings about a caulking phenomenon due to the rise in temperature. As a result, there has been a problem that a smooth supply of the fuel oil is interrupted, and in the worst case, it is not possible to use the fuel oil.